1. Field of the Invention
The present invention relates to a numerical control apparatus for a grinding machine which is capable of grinding a taper portion of a workpiece along with a non-taper portion thereof.
2. Description of the Background
In general, a cylindrical portion of a workpiece is ground by a grinding surface which is formed on a periphery of a grinding wheel in parallel relation with a rotational axis of the workpiece. In order to grind a taper portion of a workpiece with high accuracy and low degree of surface roughness, it is necessary to form a taper grinding surface on the grinding wheel which is parallel with a surface of the taper portion of the workpiece to be ground, or, instead to swivel a work table supporting the workpiece in a horizontal plane so as to make the taper structure of the workpiece parallel with the cylindrical peripheral surface of the grinding wheel.
In a conventional numerical control apparatus for a grinding machine, when grinding a workpiece which has a taper portion and a non-taper portion to be respectively ground, it is impossible to automatically and successively grind the taper portion and the non-taper portion, because such numerical control apparatus does not have the capability of initiating a truing operation for forming a taper grinding surface on the grinding wheel between successive grinding operations on the workpiece.
Therefore, to grind such workpieces in lots, non-taper portions of workpieces are ground first. Then the taper grinding surface is formed on an edge portion of the grinding wheel with a truing tool, or instead, a work table is swiveled so as to make the taper surface of the workpiece parallel with the cylindrical surface of the grinding wheel. After that, taper portions of the workpieces are ground, the non-taper portions thereof having been previously ground.
As a result, in such a conventional numerical control apparatus grinding machine, each workpiece in a lot needs to be unloaded from the machine after the non-taper portion thereof is ground, then the machine is arranged for grinding the taper portion and the workpieces are again loaded one after another in the machine for grinding of the taper portion, resulting in an inefficient time and labor consuming grinding operation.